Alright not to sound like a dick but did you pull the RPO codes to get the 4.10 ratio?? your speedo is probably closer to accurate now than before thanks to the fact that GM speedos are usually off by about 3-5mph. As to everything else yes it is still reading correctly.

with the 285/70/17's you increased tire diameter by 1 inch, so yes your speedo will be off some, about 2 miles per hour (reading faster than you are actually travelling) your tach will still be accurate. should reduce RPMs about 100 rpms (at 60 with a 1:1 ratio)

i have original sticker. 4:10 was an option.thanks for the help. i just added a gm performance exhaust, not real happy. it drones @highway speed. seems to have lost some power and definitely about 2 mpg,s.?

i have original sticker. 4:10 was an option.thanks for the help. i just added a gm performance exhaust, not real happy. it drones @highway speed. seems to have lost some power and definitely about 2 mpg,s.?

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sorry to hear about not liking the gm exhaust. Then my first post had the right info on the effective gear ratio, speedo etc. a 3.97 effective gear ratio, should read 2 mph faster than actual. so should show better mpg's but not actual. How big is the exhaust pipe on the new exhaust. if you go too big it gets rid of too much back pressure and can effect power. If its a true dual 2.5-3" diameter is about the largest you want to go